GB1303181A - - Google Patents

Abstract

1303181 Cathode-ray tube displays COMPUTER OPTICS Inc 12 March 1970 [12 March 1969] 11851/70 Heading H4T Each of the three beams of a display cathoderay tube (Fig. 2) is intensity modulated by character data information as they are scanned in an interlaced line raster by a common scanning means 4 to produce blocks of text information (Fig. 1) each comprising three text lines each composed of twenty horizontal line traces. This is achieved by superimposing on the vertical sweep an auxiliary sweep (linear ramp) termed a " diddle " sweep the period of which corresponds to the time required to scan ten horizontal traces (see Figs. 3A, 3B, 3C) so that the line spacing is compressed during the scanning of the traces forming each text line and is increased between the text lines. By this means the size of the characters is reduced without altering character definition and the number of characters displayed (by each gun) may therefore be increased without increasing the operating frequency or bandwidth of the system. Fig. 6, shows the general scheme in which data specifying the characters to be produced by each gun A, B, C, and derived from a circulating memory 30 is fed to respective registers 31, 32, 33 during the tracing of alternate text blocks and to respective registers 34, 35, 36 during the tracing of intervening text blocks the loaded register being read out into a character generator 70 as the other register is being loaded. The character generator produces beam bright-up signals which are fed via respective gates 71, 72, 73 to the respective control grids of the guns A, B, C the gates being switched to produce twenty-four horizontal increments for each character position selected adjacent ones of which pass the bright-up signals so that the characters are formed as shown in Fig. 4 in respect of the character " O " by the bright-up of certain of the increments X1 to X24 during the odd and even horizontal traces Y1 to Y16. (The upper sixteen traces are used in the formation of upper case letters and numerals and the lower four lines are used to form the stems of lower case letters.) The character data comprises six bit words per character and the registers 31 to 36 each have 128 stages through which the data is circulated so that six bit words for each of 100 characters (forming one text line, 28 character periods being utilized for horizontal retrace) are successively applied to the character generator 70 in parallel form. The system operates at conventional television line and field scanning raster under the control of a clock 20. A portion of the character generator used in the formation of the capital letter " O " is described with reference to Fig. 7, not shown.